Premature infants, especially those under 1500 grams in birth weight, suffer from frequent prolonged apneic spells. Work on the present proposal has demonstrated that these infants have active chemoreceptor tone for oxygen and have appropriate cerebrospinal fluid pH and PCO2. The smallest infants studied fail to respond to increased CO2 tensions with as great an increase in minute volume as older, more mature infants. This lack of response is associated with abnormal lungs in some infants, as these infants fail to increase ventilation but do increase respiratory work. This indicates an active respiratory center in the presence of abnormal lungs. Other infants fail to increase respiratory work, suggesting an inactive respiratory center. Ability to differentiate these infants will lead to more specific therapy for apneic premature infants. In addition, apnea of prematurity appears to be a human model of crib death (SIDS). Studies which allow a more adequate description of apneic premature infants may also permit screening of apparently healthy infants for risk of SIDS, and may allow more detailed studies to be made of the pathophysiology of this condition. BIBLIOGRAPHIC REFERENCES: Krauss, A.N. Control of breathing, in "Pulmonary Physiology of the Fetus, Newborn Infant and Child", ed. by E. Scarpelli and P.A.M. Auld, 1975, Lea and Febiger, Philadelphia. Pp. 183-194.